Multiple sclerosis, also known as sclerosis multiplex, is a chronic autoimmune disease of the central nervous system that occurs in over 2.9 millions individuals worldwide, most commonly in young to middle-aged adults, with a greater prevalence in females than males and in higher latitudes. There are different types of multiple sclerosis, varying in the presence and frequency of relapses and remissions. Various risk factors for the disorder have been identified as well – both modifiable and unmodifiable. Although many remain elusive, there are multiple theories regarding them. The causes of multiple sclerosis are yet to be established but a family history of the disease may increase the risk, and also environmental factors are believed to play a role. This paper focuses on the potentially modifiable factors. The most common theory seems to postulate an association between the disorder and viral infections, especially in individuals with Epstein–Barr virus infection, but also human herpesvirus 6, varicella-zoster virus, cytomegalovirus, or John Cunningham virus. Other risk factors include vitamin D insufficiency, or even its low levels, as multiple sclerosis is more frequent in higher latitudes. Obesity, especially during childhood and adolescence, can also be a risk factor of so-called paediatric-onset multiple sclerosis. Obesity is also linked to a higher severity of multiple sclerosis in adults. Risk factors associated with a potentially lower risk, or even some positive effects, include alcohol and caffeine consumption, as well as smoking and oral tobacco use.